Hiya, my semester finally ended and I'd like to focus my summer in improving my art. I do sketches, and from there I really don't go too far after that. u.u I'm not really use to digital art yet, the coordination between the computer and I is a little conflicting.
So I was wondering if I could have tips and such, and major criticism on my pieces. I use Paint Tool SAI and a Wacom Creative tablet.
Recentish to recent samples:
(I'm not great with coloring, these were color practice.)
(Line art practice, my enemy)

Hello, so far I think it's really great that you are starting to practice and doing practice pieces. I'm new to digital art myself so I think practice is extremely important.
These look great so far, I love your colors! My automatic suggestion for everyone is; use references for everything. constantly. all the time. for the rest of your life. The more references you use, the better your brain gets at recognizing how things are supposed to look, and the better you get at imagining things and drawing things without references. You're doing great for just starting to do digital stuff. Just keep drawing and drawing and drawing!

[.Spyro]
Nice stuff! I'm gonna' back what HoleWeet said, sources are a great thing to have, even for cartoon and chibi stuff. There's no shame in using source pics for your art, it's a big help with anything really. Hmm, if you would like some critique then I'd say to focus on stronger anatomy. By that I mean figure out where things connect and how they would look at different angles. A few of the necks and limbs looks just a bit off, but easy to fix. The best way to improve? Just keep on drawing. The more you draw out your OCs and such, the more you figure out their design. And don't forget to study how anatomy works with animals; take the time to doodle little sketches from photos of all sorts of stuff. You will retain that knowledge, and in turn it will help any kind of your work.
Hope that was some help. Keep it up!
Your art isn't too bad, but I agree with the rest when they say use references. By references, you shouldn't copy the whole picture. Use various different references to create one whole image. A lot of people seem to clump referencing with copying, but they should be separate entities here. Don't just draw the reference and be done with it either. Study it. Examine why the thing looks like that. Tear the thing apart until you understand what is going on. Copying does improve your drawing, but it does so at a much slower rate than if you're actually studying it.
I have no idea how old you are, so I can't outright say to go out there and go to live model sessions. If you're not comfortable drawing naked people, please don't push yourself. There's nothing wrong with drawing covered people(you get to study how clothes work. Hey! :V). And don't just study from reference and anatomy. GO OUTSIDE. You learn a lot of amazing things by going outside and drawing outside. Like how people sit at cafes, and all the different ways people walk. How tree branches look, how birds fly. Lots of knowledge is out there. You can also see how colors work in the real world too. Makes painting things a lot easier. For linework, I can't explain the exercises I use to improve my linework well, so I'll just give you a link I used a long while back that definitely helped improve my lines: http://drawabox.com/lesson/1 You can use the AB point for lines to make arches too. Arches are a bit harder tho.